This team is very solid, with a great Defensive core and offensive threats. However, I would argue that having both Calyrex-S and Lunala is overkill, especially as Life Orb Astral Barrage obliterates most Necrozma-DM variants. Therefore, I would suggest replacing Lunala with either defensive Xerneas or Zygarde to better handle Marshadow. Currently this team has no switchin to Life Orb or Banded Marshadow's attacks. Eternatus is cleanly 2HKOed by banded as can be 2HKOed by Life Orb as well after some chip. Xerneas handles Zygarde very well, while Zygarde can also deal with Groudon.
Xerneas @ Leftovers
Ability: Fairy Aura
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Moonblast
- Rest
- Aromatherapy
- Thunder Wave / Toxic
Zygarde @ Leftovers
Ability: Power Construct
EVs: 204 HP / 248 Def / 56 Spe
Impish Nature
- Glare / Toxic
- Thousand Arrows
- Haze / Coil
- Rest
Haze can be used to always beat Bulk Up + Spectral Thief Marshadow 1v1, however Coil can also be great for other threats.
Toxic is niche but can cripple Lunala if it tries to switch in.
Other minor changes:
- If not running Xerneas, changing Zacian's fourth move to Play Rough is a nice option for destroying Zygarde. On a Necrozma-DM switchin, you can always force it to recover with Close Combat and then proceed to destroy something with Calyrex-Shadow.
- For Dusk Mane, consider Thunder Wave over Knock Off if not running paralysis on the Xerneas / Zygarde. It can cripple threats like Calyrex-S upon switchin.
- For Yveltal, reduce Speed a bit to Slow Turn (either minSpeed Sassy or 25 Speed IV Careful)
- Calm Nature > Timid Nature on Eternatus; 44 Speed and a neutral nature is used just to outspeed Timid Kyogre. Alternatively, you can try to outrun Adamant Marshadow with 92 Speed and Timid.
So those are all my opinions on this team; say something if you think I missed something lol. I hope I helped!